The two major presidential candidates left standing would make major changes to the national security and foreign policies carried out by the George W. Bush administration over the last seven years. Not surprisingly, exactly what kind of changes depends on who ends up on the steps of Capitol Hill taking the oath of office in January 2009 -- Sen. John McCain (R-AZ) or Sen. Barack Obama (D-IL).

The following analysis is based on several indicators: the candidates' U.S. Senate voting records; their national security platforms as laid out in articles, op-eds and speeches; and their responses to queries in debates, public appearances, and questionnaires. Although campaign pledges and voting records do not always accurately translate into actual policy, they can provide important clues as to the future president's inclinations.

IRAQ WAR

The war in Iraq has produced the sharpest divisions between the two candidates on the 2008 campaign trail. When the next president takes office, he will face major decisions about Iraq, where the United States will have been for almost six years, and where it is likely that upward of 140,000 U.S. troops will still remain.

John McCain cosponsored the 2002 vote to authorize the use of force against Iraq, arguing at the time that Saddam Hussein was "a threat of the first order." Although he was a vehement critic of the administration's "mismanagement and failure" during the early war years, he advocated the surge of additional troops to Iraq and the need to stay as long as necessary to win the war. He joined with Sen. Joseph Lieberman (I-CT) to pen an op-ed in the Wall Street Journal entitled "The Surge Worked." He has suggested that his Democratic opponents advocate "surrender" by calling for a withdrawal timetable and billed his campaign as the "No Surrender Tour." McCain has proposed that the U.S. military's 50-plus years in South Korea, Japan and Germany is a good model for Iraq.

In 2002, when he was an Illinois state senator, Barack Obama opposed the war. However, after he was elected to the U.S. Senate, he voted against early proposals by Sen. Russ Feingold (D-WI) and others to set a timetable for withdrawal; now Obama votes consistently in favor of establishing a timetable. Obama's plan for exiting Iraq would send home one or two combat brigades a month, with most combat troops out by the end of 2009. At an MSNBC debate in September 2007, Obama refused to guarantee that he would have all U.S. forces out of Iraq by the end of his first term. Obama has also opposed permanent bases in Iraq.

IRAN POLICY

President Bush has displayed unremitting hostility toward the radical regime dominating Iran, a country that U.S. intelligence sources report had previously been pursuing a nuclear weapons program. He branded Iran part of the "axis of evil" and promoted regime change as the preferred U.S. policy. With a few limited exceptions, the United States under Bush has refused to talk directly with Iran.

McCain has been clear about his position on Iran. In February 2008, he told an audience: "I intend to make unmistakably clear to Iran we will not permit a government that espouses the destruction of the State of Israel as its fondest wish and pledges undying enmity to the United States to possess the weapons to advance their malevolent ambitions." He also rejects "unconditional dialogues" with Iran.

Obama has delivered messages on Iran that were more mixed. He has said "The danger from Iran is grave, it is real, and my goal will be to eliminate this threat." In a June 2008 speech to the American-Israel Public Affairs Committee, he refused to take the military option against Iran off the table: "I will always keep the threat of military action on the table to defend our security and our ally Israel. Sometimes there are no alternatives to confrontation. But that only makes diplomacy more important. If we must use military force, we are more likely to succeed, and will have far greater support at home and abroad, if we have exhausted our diplomatic efforts."

In the same speech, however, Obama promised: "aggressive, principled diplomacy without self-defeating preconditions, but with a clear-eyed understanding of our interests." He has said also that it "would be a profound mistake for us to initiate a war with Iran" and condemned the administration's "saber-rattling" on Iran. Obama missed a vote on a controversial amendment offered by Sen. Jon Kyl (R-AZ) and Lieberman that proposed labeling Iran's Islamic Revolutionary Guard a terrorist organization. Obama called the amendment a repeat of the mistakes that led to war in Iraq; however, he had cosponsored an earlier bill declaring the Revolutionary Guard a terrorist organization.

NUCLEAR WEAPONS

World free of nuclear weapons: In 2007, a bipartisan group of senior and former government officials called for moving toward a "world free of nuclear weapons." In their article by that name, former Secretary of State Henry Kissinger, former Secretary of State George Shultz, former Sen. Sam Nunn (D-GA) and former Secretary of Defense William Perry urged the United States to lead an international effort to rethink traditional deterrence, reduce nuclear weapon stockpiles and take other steps toward the longer term goal of a nuclear-weapon-free world.

Obama has been clear in his support of their effort. In response to a Council for a Livable World questionnaire, he promised: "As president, I will take the lead to work for a world in which the roles and risks of nuclear weapons can be reduced and ultimately eliminated."

In a May 2008 speech, McCain also endorsed the concept: "A quarter of a century ago, President Ronald Reagan declared, 'our dream is to see the day when nuclear weapons will be banished from the face of the Earth.' That is my dream, too."

New nuclear weapons: The Bush administration has put forward proposals to build a new generation of nuclear weapons; however, these plans might be seen as conflicting with U.S. efforts to restrain other states' nuclear ambitions. McCain has supported the proposed new nuclear weapons programs. In four key Senate votes from 2003 to 2005, McCain voted to proceed with the work on such weapons. But in his May 2008 speech, he declared: "I would cancel all further work on the so-called Robust Nuclear Earth Penetrator, a weapon that does not make strategic or political sense." McCain did not express an opinion on another new nuclear weapons program, the Reliable Replacement Warhead. Obama, only in the Senate for the fourth vote, opposed the new weapons. He has not been categorical in response to the Council for a Livable World's queries about his position on new nuclear weapons, responding that he did not support "a premature decision to produce the [Reliable Replacement Warhead]."

Nuclear Comprehensive Test Ban Treaty (CTBT): One of the longest sought goals of the nuclear age has been a global ban on all nuclear test explosions as an important step to advance nuclear nonproliferation. In 1996, after 50 years of work, the Comprehensive Test Ban Treaty was signed and opened for ratification. However, three years later, the Senate decisively rejected the treaty. Although the United States has not conducted a nuclear test explosion since 1992, the Bush administration has not put the treaty forward for a new vote.

McCain voted against the treaty, stating at the time: "The viability of our nuclear deterrent is too central to our national security to rush approval of a treaty that cannot be verified and that will facilitate the decline of that deterrent." More recently, McCain has committed to continuing the moratorium on nuclear weapons testing that has existed since 1992, and promised to take "another look" at the test ban treaty. Although Obama was not in the Senate at the time of the 1999 vote, he has promised to make the test ban treaty a priority of his first term in office and pledged to work to rebuild bipartisan support for the treaty.

Nuclear non-proliferation: Efforts to prevent the spread of nuclear weapons to additional countries have faltered during the Bush administration. McCain has promised expanded proliferation efforts, increasing funding for American non-proliferation programs, strengthening international treaties and institutions to combat proliferation, increasing funding for the International Atomic Energy Administration and negotiating a Fissile Material Cut-off Treaty.

Obama has committed to securing all vulnerable nuclear weapons materials around the world within four years of taking office: "I'll lead a global effort to secure all loose nuclear materials during my first term in office." He has also promised to seek a global ban on the production of fissile materials for nuclear weapons and "dramatic reductions" in nuclear weapons stockpiles and a strengthened Nuclear Non-Proliferation Treaty.

MISSILE DEFENSE

In 2001, the Bush administration withdrew from the 1972 Anti-Ballistic Missile (ABM) Treaty and since then has moved swiftly to deploy national missile defense interceptors in Alaska and California. The latest fiscal budget request for 2009 is $12.3 billion for all forms of missile defense.

McCain has declared that he "strongly supports the development and deployment of theater and national missile defenses." His votes in the Senate back up that claim: he opposed all three amendments to cut the program in 2004. In a 2001 speech to the Munich Conference on Security Policy, he advocated abandoning the ABM Treaty.

Obama has been critical of the Bush missile defense plans: "The Bush Administration has in the past exaggerated missile defense capabilities and rushed deployments for political purposes." Obama voted for an amendment offered by Sen. Carl Levin in 2005 (the last major vote on missile defense) while McCain missed the vote. Obama has not indicated plans for missile defense upon assuming the presidency.

Missile defense site in Europe: McCain has also been clear in his support for a third missile defense site in Europe that is bitterly opposed by Russia. Congress cut a portion of the funding for the program in 2007 in advance of approval from the two Central European countries. In an October 2007 debate, McCain said: "I don't care what [President Vladimir Putin's] objections are to it." He has also described the system as a "hedge against potential threats" from Russia and China.

Obama has been less clear what he would do with the Bush proposal, but indicated that he would not allow the program "to divide 'new Europe' and 'old Europe.'" He also suggested that: "If we can responsibly deploy missile defenses that would protect us and our allies, we should -- but only when the system works."

NORTH KOREA

During the last seven years, it is believed that North Korea reprocessed enough plutonium for about six to ten nuclear weapons. In 2006, North Korea became the ninth country in the world to test a nuclear weapon. In the last 12 months, negotiations among six countries -- the six-party talks including the United States, North Korea, Russia, China, Japan and South Korea – produced an agreement where North Korea would disable its facility and provide a full declaration of its nuclear sites and activities. In exchange, the United States would beging the process of removing North Korea from the terrorist list, easing economic sanctions and moving toward normalization of U.S.-North Korea and Japan-North Korea relations.

After President Bush announced on June 26 that North Korea would be taken off the state-sponsored terrorism list in response to North Korea's declaration of its nuclear program, Obama called the move "a step forward." He went on to say: "We should continue to pursue the kind of direct and aggressive diplomacy with North Korea that can yield results. The objective must be clear: the complete and verifiable elimination of North Korea's nuclear weapons programs."

McCain was a bit less effusive, calling the announcement "a modest step forward." He added: "Our goal has been the full, permanent and verifiable denuclearization of the Korean Peninsula . . . If we are unable to fully verify the declaration submitted today and if I am not satisfied with the verification mechanisms developed, I would not support the easing of sanctions on North Korea."

OTHER ISSUES IN BRIEF

Closing Guantanamo Bay prison:Obama and McCain agree: Close the prison.

U.S.-India nuclear deal: McCain and Obama both voted for the U.S.-India nuclear deal in 2006, but Obama also voted for amendments to condition the deal on India ending military cooperation with Iran and a presidential certification that nuclear cooperation with India will not aid India in making more nuclear weapons. McCain continues to endorse the treaty "as a means of strengthening our relationship with the world's largest democracy, and further involving India in the fight against proliferation."

Military forces:McCain and Obama have both called for expanding the size of our active duty military forces.

John Isaacs is the Executive Director of the Center for Arms Control and Non-Proliferation where his work focuses on national security issues in Congress, Iraq, missile defense, and nuclear weapons. Isaacs has published articles in the New York Times, Los Angeles Times, Atlanta Journal, St. Louis Post Dispatch, Christian Science Monitor, Nuclear Times, Arms Control Today, American Journal of Public Health, and Technology Review.